The compressed tablet is one of the oldest and most popular unit dosage forms for medicinal substances. The tablet as a dosage form can be traced to well over 1,000 years ago when a procedure for molding solid forms containing medicinal ingredients was recorded. As a result of the introduction of new carriers and compression vehicles, tablets are replacing many forms of pills, powders and capsules. Accordingly, tablets presently represent the largest production volume of all pharmaceuticals.
The reasons for the widespread use of tablets are apparent, since tablets facilitate: (1) administration of medication in an accurate dose; (2) fast and accurate dispensing with less chance of error and contamination: (3) ease of administration: (4) administration in a form in which the time and area of contact between the active ingredient and the taste buds are reduced, thus obviating the physiological problems associated with the oral administration of drugs that possess a bitter taste and, in the case of coated tablets, with drugs that possess a disagreeable odor; (5) release of drugs at specific locations in the gastro-intestinal tract to prevent degradation of drugs sensitive to the low pH environment in the stomach, prevent release of drugs that irritate the gastric mucosa in the stomach, and facilitate local action or preferential absorption at specific sites in the tract: (6) enhanced stability by effecting a marked reduction in the surface of the drug exposed to the environment; (7) rapid production; and (8) economy and ease in storage, packaging and shipping.
There are currently three basic methods for tableting. They are the wet granulation method, the dry granulation method and the direct compression (DC) method. The direct compression method is by far the desired method from the standpoint of processing time and requirements of equipment and materials. However, only a very limited number of pharmaceutical substances possess enough cohesive strength and flowability to allow direct compression without previous granulation. Certain crystalline materials, such as potassium bromide and potassium chloride can be compressed without preliminary treatment. Also, drugs such as aspirin and phenolphthaline can be directly compressed after blending with suitable tableting excipients.
It has been estimated that about 20 percent of the materials used for tableting in the pharmaceutical field may be compressed directly. In order to use this method to a greater extent, many more materials are modified either by treating the material in some special way during early stages of preparation, or by adding a direct compression vehicle, i.e., a dry binder or excipient material which will mix with the active ingredient to provide a flowable powder and form an easily compressible carrier. Exemplary United States patents relating to directly compressible tablets include U.S. Pat. No. 3,584,114 to Cavalli, et al., U.S. Pat. No. 3,725,556 to Hanssen, et al., U.S. Pat. No. 3,873,694 to Kanig, U.S. Pat. No. 4,072,535 to Short, and U.S. Pat. No. 4,439,453 to Vogel.
There are currently several available binders or excipients which can be used as direct compression vehicles. They include spray-dried lactose; anhydrous lactose: microcrystalline cellulose; dicalcium phosphate dihydrate, unmilled; spray-congealed mannitol; ungelatinized starch (e.g., corn starch), and partially or fully pregelatinized starch.
Starch, as defined by the National Formulary XVI, "consists of the granules separated from the mature grain of corn {Zea mays Linne (Fam.Gramineae)} or of wheat {Triticum asetivum Linne (Fam.Gramineae)}, or from tubers of the potato {Solanum tuberosum Linne (Fam.Solanaceae)}." Pregelatinized starch is defined by the National Formulary XVI as "starch that has been chemically and/or mechanically processed to rupture all or part of the granules in the presence of water and subsequently dried. Some types of pregelatinized starch may be modified to render them compressible and flowable in character." Many types of partially or fully pregelatinized starches are commercially available for use in direct compression tablet formulations.
With the advent of the above described direct compression vehicles, drug manufacturers are seeking to formulate or reformulate pharmaceutically active compounds into compositions which are directly compressible into tablets. One such compound is cyclophosphamide, an anti-neoplastic agent manufactured by Bristol-Myers Company under the trademark CYTOXAN.RTM., which is currently tableted with specially prepared directly compressible diluent. This DC diluent is produced by a wet granulation process. However, processing cyclophosphamide using wet granulation method has certain drawbacks. A major problem is that it is difficult to control the moisture of the resulting tablet. A second problem is that the dissolution rate, i.e., the rate at which the tablet dissolves in water, decreases over time. The third problem is that the dissolution rate of the tablet varies from batch to batch, with some batches having unacceptably low rates.
Obviously, a direct compression cyclophosphamide tablet would be desirable. Unfortunately, cyclophosphamide is not one of the few known compounds which possesses the cohesive strength and flowability to allow direct compression. Thus, there is a need for a directly compressible composition comprising cyclophosphamide and a direct compression vehicle, which composition obviates the problems resultant from wet processing.
Accordingly, it is an object of this invention to provide a directly compressible pharmaceutical composition comprising cyclophosphamide and a direction compression vehicle.